In current times, with increasing threats of violence, the inspection of vehicles in addition to luggage and cargo at transit points has become almost universally mandatory. In addition to passenger and cargo vehicles, contraband such as explosives, weapons, narcotics, dangerous chemicals, and nuclear and radioactive materials can also be concealed in various parts of general aircraft for illegal transportation. Detection of such contraband and presence of other threat items in an aircraft requires detailed inspection of the aircraft in its entirety.
Amongst detection systems that provide for efficient non-invasive inspection, X-ray imaging systems are the most commonly used. Transmission based X-ray imaging systems are traditionally used to inspect trucks and cargo containers for contraband. Inspection of a complete aircraft however, can be challenging with a transmission-based geometry wherein typically, the source is located on one side of the aircraft and detectors are located on the other side of the aircraft. This geometry has many challenges, and in particular, when scanning around the landing gear and engines as there is difficulty placing detectors and thus, in producing radiographic images.
In backscatter based inspection systems, X-rays are used for irradiating a vehicle or object being inspected, and rays that are scattered back by the object are collected by one or more detector arrays. The resultant data is appropriately processed to provide images which help identify the presence of contraband. In transmission systems, the radiation source is placed on one side of the object while the detectors are placed on the other side. The radiation source and detectors are maintained in fixed alignment relative to each other.
Since aircraft are typically made of lighter materials, a backscatter-based detection system would provide adequate penetration in most cases and thus would only require equipment to be placed on one side of the aircraft. However, backscatter technology may not be suitable when all areas of the aircraft have to be penetrated with a high detection probability, such as is the case with nuclear materials detection. Areas of high attenuation as measured by the backscattered radiation include fuel tanks, transformers, counterweights, among other aircraft components. In addition, backscatter technology cannot effectively discriminate between typical metals and special nuclear materials.
Aircraft inspection calls for unique requirements such as the capability of inspecting large aircraft from more than one side. In addition, varying aircraft sizes would require the inspection head to scan at different heights, and several sections of the aircraft, such as the wings and tails, would require different head and detector scanning configurations. Conventional X-ray backscatter and transmission systems, however, do not have adequate scanning robustness, ability to work in various orientations, scanning range, or field of view for aircraft inspection applications.
Therefore, what is needed is a rapid and accurate inspection system for determining the presence of concealed illegal materials, both nuclear and non-nuclear, in general aviation aircraft.
What is also needed is a system that is easily transportable, mobile, and non-intrusive, that is capable of operating even in rugged outdoor conditions such as airport environments.